Field
Embodiments of the present disclosure relate generally to power conversion, and, in particular, to a three port converter with dual independent maximum power point tracking and dual operating modes.
Description of the Related Art
Resonant converters provide many advantages over other types of power converters. Such advantages may include low noise, low component stress, low component count, and predictable conduction-dominated losses. Resonant converters may therefore be smaller, less costly, and more efficient devices that other types of converters.
Converters are often used in power generation for distributed generators such as photovoltaic (PV) panels or modules that produce DC voltage. The PV modules are conventionally connected in series and generate power at varying rates depending on operating factors such as the environment. Typically, a Maximum Power Point Tracking (MPPT) algorithm will find the optimum operational point in order to extract the maximum power from the series string of PV modules. During power generation among multiple PV panels, varying amounts of DC voltage may be generated over a particular time period.
FIG. 1 is a schematic diagram of a series connected resonant converter in accordance with the related art. FIG. 1 depicts a converter 100 coupled to a voltage source 102 comprising two voltage sources (105 and 110) in series, connected in parallel to a bridge circuit 122. The bridge circuit 122 is comprised of four switches (120, 125, 130, 135) coupled in an H-bridge configuration to a first side of a transformer 150. Switches 120 and 125 are connected through an inductor 140 to a first terminal of the transformer's primary winding, and switches 135 and 130 are connected to a second terminal of the primary winding via a series capacitor 145. The transformer 150 passes power from a secondary winding to a three phase AC switching circuit 126 and ultimately to respective three phase outputs 198. The AC switching circuit 126 comprises two transistors (155/160) in series with a first capacitor 185, the combination coupled in parallel with mirrored transistors (165/170) that are in series with a second capacitor 190, and also with transistors (175/180) that are in series with a third capacitor 195. A node is connected between each pair of transistors in the AC switching circuit 126 and the corresponding capacitors to connect and form each line of the three phase output 198.
The series-connected voltage sources 105 and 110, which may be a string of multiple PV modules, provides more power for conversion than a single PV module. Since the PV modules are coupled in series though, MPPT must be performed on the combined pair of PV modules, which is less efficient than MPPT at the individual panel level. Additionally, the series-connected string of PV modules is capable of creating a high enough voltage potential to be able to sustain an electrical arc should the DC current be interrupted by virtue a faulty connector or wire conductor. An arc of this type has the potential to start a fire in the DC circuit wiring that could spread to other parts of the system or the building that the PV system is installed upon. Safety legislation stipulates that if the total DC voltage generated by a series string of PV modules exceed 80 volts then some form of arc detection and protection is needed, requiring additional circuitry to be added to the converter in order to protect the system from any potential arc that could cause a fire in the DC circuit.
Therefore, there is a need in the art for a method and apparatus for efficiently converting power from a plurality of DC sources.